In 1956, Rosvold, Mirsky, Sarason, Bransom and Beck, developed the first continuous performance test (CPT), a task of visual attention that measured an individual's ability to sustain performance over time, termed vigilance. Since that original CPT, several variants of the test have been developed, often with good reliability in distinguishing individuals without neurological impairment from those with attention deficit/hyperactivity disorder, schizophrenia, traumatic brain injury, dementia, Parkinson's disease, and developmental dyslexia, to name a few (Riccio, C. A., Reynolds, C. R., Lowe, P. A. (2001). Clinical applications of continuous performance tests: Measuring attention and impulsive responding in children and adults. New York: Wiley).
Many continuous performance tests function through the visual medium, displaying stimuli to which participants are instructed to respond or ignore based on some salient features of the stimuli. For example, in the Conners' Continuous Performance Test (Conners, C. K. (2000). Conners' Continuous Performance Test (CPT-II): Computer program for Windows, technical guide and software manual. Multi-Health Systems New York), a stimuli that should not receive a response (noise stimuli) is a single letter ‘X’ on the screen, while all other single letters on the screen should receive a response (target stimuli). Another popular CPT, the Cornblatt Identical-Pairs CPT (Cornblatt, B. A., & Kelip, J. G. (1994). Impaired attention genetics, and the patho-physiology of schizophrenia. Schizophrenia Bulletin, 20 (1), 31-46) assigns target stimuli to a number or image that repeats twice.
From the results of several trials, CPT tasks are used to measure several components of executive function. Executive function includes the sustaining of attention, maintaining of response sets, set-shifting, problem solving, and planning and following through on tasks (Cohen, R. A. (1993). Attentional control: Subcortical and frontal lobe influences. In R. A. Cohen (Ed.), The neuropsychology of attention (pp. 219-254). New York: Plenum Press).
While neuropsychological models of executive function and attention contain areas throughout the brain, the majority of the components are contained in the frontal lobe and its projections. Individuals with focal frontal lobe damage most often complain of difficulties in attention and concentration (Riccio, C. A., Reynolds, C. R., Lowe, P. A. (2001). Clinical applications of continuous performance tests: Measuring attention and impulsive responding in children and adults. New York: Wiley).
Visual CPT tasks tend to rely on stimuli that, based on current understanding of the visual system, intrinsically trigger several visual pathways. However, deficits in a participant's visual system would likely reduce CPT task performance, indicating that the task is in fact not fully measuring visual attention, but visual function as well.
For example, presume a stimulus presentation on a typical CPT task. When a CPT stimulus spontaneously appears on the screen, the hard boundaries between the character's edge and background and sudden large-scale changes in luminance in the regions of the character are likely to trigger a magnocellular response in an individual with intact magnocellular function. The magnocellular response is faster than the response of other cells. Therefore, on average, an individual with deficient magnocellular function will perceive the appearance of the character more slowly and therefore will respond later. However, the individual's attention may still be strong, but inaccurately measured as deficient.
Visual dysfunction is noted in many disorders. Magnocellular-pathway deficits are noted to occur in developmental dyslexia (Omtzigt, D., Hendriks, A. W., & Kolk, H. H. J. (2002). Evidence for magnocellular involvement in the identification of flanked letters. Neuropsychologia, 40, 1881-1890). NMDA-based non-linear contrast gain control (Zemon, V., Butler, P. D., Gordon, J., Jalbrzikowski, M., Javitt, D. C., Piesco, J., Russo, J., & Schechter, I. (2004). Neural dysfunction in schizophrenia: contrast-response functions and a nonlinear model, Program No. 347.122004 Abstract Viewer and Itinerary Planner. Washington, D.C. Society for Neuroscience, Online; Butler, P. D., Zemon, V., Schechter, I., Saperstein, A. M., Hoptman, M. J., Lim, K. O., Revheim, N., Silipo, G., & Javitt, D. C. (2005). Early-Stage Visual Processing and Cortical Amplification Deficits in Schizophrenia. Archives of General Psychiatry, 62 (5), 495-504; Kwon, Y. H., Nelson, S. B., Toth, L. J., & Sur, M. (1992). Effect of stimulus contrast and size on NMDA receptor activity in cat lateral geniculate nucleus. Journal of Neurophysiology, 68, 182-195) and magnocellular deficits (Butler, P. D., Zemon, V., Schechter, I., Saperstein, A. M., Hoptman, M. J., Lim, K. O., Revheim, N., Silipo, G., & Javitt, D. C. (2005). Early-Stage Visual Processing and Cortical Amplification Deficits in Schizophrenia. Archives of General Psychiatry, 62 (5), 495-504; Schechter, I., Butler, P. D., Silipo, G., Zemon, V., & Javitt, D. C. (2003). Magnocellular and parvocellular contributions to backward masking dysfunction in schizophrenia. Schizophrenia Research, 64, 91-101) are found in schizophrenia. Magnocellular, parvocellular, and koniocellular deficits are found in Parkinson's disease (Silva, M. F., Faria, P., Regaterio, F. S., Forjaz, V., Januario, Freire, A., Castelo-Branco, M. (2005). Independent patterns of damage within magno-, parvo- and koniocellular pathways in Parkinson's disease. Brain, 128 (10), 2260-2271). In traumatic brain injury, magnocellular deficits are noted in children with extremely low birth weights (Downie, A. L., Jakobson, L. S., Frisk, V., Ushycky, I. (2003). Periventricular brain injury, visual motion processing, and reading and spelling abilities in children who were extremely low birthweight. Journal of the International Neuropsychological Society, 9 (3), 440-449), and cortical gain control deficits are noted in adults (Du, T., Ciuffreda, K. J., Kapoor, N. (2005). Elevated dark adaptation thresholds in traumatic brain injury. Brain Injury, 19 (13), 1125-1138).
Therefore, this invention was developed, based on the current understanding of the visual system, to provide a novel method to assess visual attention in each visual pathway discretely. The invention aims to provide a more accurate representation of the contributive roles of visual function and visual attention in a participant's performance.